A conventional lower ferrule or runner 12 slidably held on a central shaft 1 of an umbrella as shown in FIG. 4 includes a fastening steel wire 3 fastened on the ferrule 12 for pivotally securing a plurality of ribs 2 of the umbrella. Two free wire ends 30 of the wire 3 will be twisted for tying a knot of the two free wire ends 30 to be kept on the ferrule 12. The wire end 30 after being cut will form an acute tip to easily prick an umbrella user or a factory assembly worker to cause pricking injury to the user or worker. Meanwhile, the acute wire ends 30 remarkably existing on the umbrella ferrule may influence a decorative appearance and product quality of the umbrella.